362 J. B. JOHNSTON 
which leaves no reasonable ground for doubt that the body in 
question is the homologue of the primordium hippocampi as 
described in fishes and amphibians. 
There is no ground whatever for Professor Herrick’s assumption 
(10, p. 473) that the greater part of this body belongs to the epi- 
thalamus, while a smaller rostral portion represents the primordium 
hippocampi. 
The fact of greatest interest regarding this body is, perhaps, 
that the primordium of the visceral cortical complex of higher 
animals (hippocampus, fornix, and related structures) remains in 
cyclostomes in the telencephalon medium. As has been pointed 
out in previous papers (710 ¢, ’11 a) the hemisphere evagination in 
vertebrates involves at first only the primary olfactory centers and 
it is only in later stages of phylogeny that the cortical substance 
is evaginated. 
Anterior pallial commissure 
This has been known as the dorsal olfactory decussation, the 
dorsal part of the anterior commissure, and by other names. 
Schilling speaks of this as the anterior commissure and makes 
only minor mention of the true anterior commissure. Schilling 
recognizes in this dorsal commissure fibers connecting the formatio 
bulbaris of the two sides and fibers connecting each formatio bul- 
baris with the opposite lobus olfactorius. The writer has described 
fibers connecting the lobus of one side with the opposite primor- 
dium hippocampi. In addition, there are to be mentioned fibers 
which come to the commissure from the area of union of the caudal 
wall of the hemisphere with the telencephalon medium (fig. 22). 
A certain determination of the nature of these fibers depends 
on the further study of the region from which they arise. ‘They 
may correspond to the fibers in selachians to which the writer has 
given the namé corpus callosum. ‘The matter of greatest moment 
in this connection is the existence in the lowest order of verte- 
brates of a commissure located in the lamina supraneuroporica. 
The writer has shown elsewhere that the corresponding commissure 
in selachians is large and important, and must reiterate the view 
that this dorsal or supraneuroporic commissure is primitive and 
